Method and device for detecting an electrical voltage in a supply network

Abstract

A method for recording the magnitude and phase of electrical voltage in an electrical three-phase supply network for a fundamental and at least one harmonic is provided. The method includes measuring an electrical three-phase voltage of the supply network, transforming the measured voltage values into polar coordinates using a rotating voltage phasor for the fundamental as a measured reference phasor, and respectively observing values of at least one voltage phasor for the fundamental and of at least one voltage phasor for at least one harmonic to be recorded with the aid of a state observer, and tracking the observed values on the basis of the measured reference phasor.

The invention claimed is: 
     
       1. A method for recording a magnitude and phase of electrical voltage in an electrical three-phase supply network for a fundamental and at least one harmonic, the method comprising:
 measuring an electrical three-phase voltage of the supply network, 
 transforming measured voltage values into polar coordinates using a rotating voltage phasor for the fundamental as a measured reference phasor, 
 respectively observing, at least in part by a state observer, values of at least one voltage phasor for the fundamental and of at least one voltage phasor for at least one harmonic to be recorded, wherein the state observer is a Kalman filter, and 
 tracking the observed values based on the measured reference phasor. 
 
     
     
       2. The method according to  claim 1 , wherein the state observer operates based on a recorded network frequency and the recorded network frequency is input to the state observer as an input variable. 
     
     
       3. The method according to  claim 2 , comprising:
 selecting, based on the recorded network frequency, an up-to-date observer matrix from a plurality of pre-calculated observer matrices, and 
 observing, by the state observer, the values of the voltage phasors using the up-to-date observer matrix. 
 
     
     
       4. The method according to  claim 1 , comprising:
 recording, by the state observer, a positive-sequence system and a negative-sequence system for the fundamental and for each harmonic to be recorded, respectively. 
 
     
     
       5. The method according to  claim 1 , comprising:
 observing a voltage phasor for a positive-sequence system and a voltage phasor for a negative-sequence system, and 
 determining the fundamental and each harmonic to be recorded based on the voltage phasor for the positive-sequence system and the voltage phasor for the negative-sequence system, respectively. 
 
     
     
       6. The method according to  claim 1 , comprising:
 measuring the electrical three-phase voltage of the supply network at a transformer connected to the electrical supply network. 
 
     
     
       7. The method according to  claim 1 , comprising:
 transforming the measured voltage values into polar coordinates using a Clarke transformation that assumes that the measured voltages are free of a zero-sequence system. 
 
     
     
       8. The method according to  claim 1 , comprising:
 recording the at least one harmonic, and 
 producing an electrical current for feeding into the electrical supply network, the electrical current comprising a compensation current component in order to reduce the at least one recorded harmonic. 
 
     
     
       9. The method according to  claim 8 , wherein the compensation current component has at least one current harmonic and a current harmonic of the at least one current harmonic is respectively determined by an amplitude and a phase and based on the observed harmonics of the recorded voltage. 
     
     
       10. The method according to  claim 9 , comprising:
 adjusting, using a controller, an amplitude of the current harmonic of the compensation current component, and 
 receiving, by the controller, as an input signal representative of a difference between a desired voltage value and an observed actual voltage value of the harmonic of the recorded voltage. 
 
     
     
       11. The method according to  claim 10 , wherein the controller is selected from a list comprising:
 a PID controller, 
 a PI controller, 
 a P controller, and 
 a PD controller. 
 
     
     
       12. The method according to  claim 8 , wherein the compensation current component is based on current harmonics as positive-sequence system and negative-sequence system components, respectively. 
     
     
       13. An inverter configured to:
 produce an electrical current for feeding into an electrical supply network, the electrical current comprising a compensation current component for reducing at least one recorded harmonic, wherein an electrical three-phase voltage of the electrical supply network is measured and transformed into polar coordinates using a rotating voltage phasor for a fundamental as a measured reference phasor, and wherein a state observer respectively observes values of at least one voltage phasor for the fundamental and of at least one voltage phasor for at least one harmonic, and wherein the observed values are tracked based on the measured reference phasor, wherein the state observer is a Kalman filter. 
 
     
     
       14. A wind power installation having the inverter according to  claim 13 . 
     
     
       15. A wind power installation configured to operate according to the method of  claim 1 . 
     
     
       16. The method according to  claim 4 , comprising:
 recording, by the state observer, a DC component. 
 
     
     
       17. The method according to  claim 5 , comprising:
 determining a DC component based on a voltage phasor, and 
 recording the DC component. 
 
     
     
       18. The method according to  claim 6 , wherein the electrical three-phase voltage of the supply network is measured at a side of the transformer that electrically faces a wind power installation which feeds the electrical supply network via the transformer.